Battery protection circuit

ABSTRACT

A protection circuit for a cellular telephone battery includes a first memory for storing battery identification data and a second memory associated with the telephone includes data relating to which battery type may be used by this telephone. When the battery is connected to the telephone, the battery identification data is compared to the battery type data stored in the telephone. The battery is automatically disconnected from the telephone if the two sets of data do not correspond to each other.

BACKGROUND OF THE INVENTION

This invention relates generally to a cellular telephone and moreparticularly is concerned with providing protection relating to the useof a battery with a cellular telephone.

In general, cellular telephones are not permitted to be used inhazardous locations such as petrochemical refineries, mines, or anyenvironment in which gas, vapours, solvents, flying fibres and dust arepresent for there is a risk that the telephone, or its battery, couldcreate an arc or a spark which could cause an explosion.

A spark could arise in a number of ways. For example an incorrectbattery could be connected to a cellular telephone and, in use, thebattery could become excessively hot, provide an over-voltage orover-current, or some other factor could arise which generates a spark.The problem is compounded in that printed circuit boards which are usedwith cellular telephones are, in their nature, of compact constructionwith very small track width and minimal track separation.

Any possible short circuit condition is of particular importance. Atypical lithium ion battery can produce as much 30 Amps on a shortcircuit condition and this can destroy the entire battery. Although itis known to make use of a protection integrated circuit in a batterypack this type of circuit limits the amount of charge and dischargecurrent but does not provide sufficient protection against abnormalconditions which can destroy the protection integrated circuit.

Another potential problem can arise when the battery is recharged. Ifthe temperature of the charger increases, for whatever reason, above apredetermined level unwanted effects can occur which can give rise tothe generation of a spark.

In the light of problems of the aforegoing type, and as a general rule,the use of a cellular telephone in a hazardous location is notpermitted.

SUMMARY OF THE INVENTION

The invention provides, in the first instance, a method of providingprotection relating to the use of a cellular telephone which includesthe steps of:

-   -   (a) storing first data, which identifies a battery which is        permitted to be used with the telephone, in a first memory in a        protection circuit which is associated with the battery;    -   (b) storing second data, which identifies the said permitted        battery, in a second memory which is associated with the        telephone; and    -   (c) allowing the said battery to power the telephone only if the        said first data corresponds to the said second data.

The method may include the step of disconnecting the battery from theprotection circuit upon the occurrence of at least one of the following:

-   -   (a) if the temperature of the telephone exceeds a predetermined        temperature; and    -   (b) if the current drawn from the battery exceeds a        predetermined current.

When the battery is recharged by a charger the temperature of thecharger may be monitored and, if the temperature of the charger exceedsa predetermined temperature, the battery may be disconnected from thecharger or the battery may be disconnected from the telephone. Bothsteps can be carried out.

The invention also extends to a protection circuit for a battery whichis used with a cellular telephone, the protection circuit including:

-   -   (a) a first memory in which is stored first data which        identifies the battery;    -   (b) a comparator for comparing the first data to second data        which is stored in a second memory associated with the telephone        and which identifies a battery which is permitted to be used        with the telephone; and    -   (c) a switch which is responsive to the comparator and which        allows the said battery to power the telephone only if the first        data corresponds to the second data.

The protection circuit may include means for disconnecting the batteryfrom the telephone if the temperature of the telephone exceeds apredetermined temperature. The said means may be a thermal fuse.Preferably the thermal fuse is also a current fuse.

A sensor may be provided for monitoring the temperature of a chargerwhich is used for recharging the battery and the protection circuit mayinclude switch means which is responsive to the sensor and which isoperable, when the temperature of the charger exceeds a predeterminedtemperature, to carry out at least one of the following:

-   -   (a) to disconnect the battery from the charger; and    -   (b) to disconnect the battery from the telephone.

The protection circuit may be encapsulated in a solid insulatingmaterial of any appropriate type e.g. a polyurethane resin.

Care is taken in selecting the battery. Preferably the battery is amanganese dioxide cell of the type sold by NEC which has the capabilityof being able to withstand a short circuit condition without exploding.This is to be contrasted with cobalt dioxide cells which are effectivelydestroyed, giving rise to unwanted sparks, if short circuited without aprotection circuit.

The battery, when used, generates hydrogen gas which must be vented toatmosphere. In accordance with a preferred feature of the invention avent cap for the battery, which is encapsulated in an insulatingmaterial, is placed at a lower region of the battery, as opposed to aposition on a side or at an upper region of the battery, so that thebattery is prevented from swelling and discharging.

The protection circuit of the invention is preferably provided incombination with the battery, as an integral unit. The battery and theprotection circuit, in combination, are preferably encapsulated in asuitable insulating material e.g. a polyurethane resin.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference tothe accompanying drawings in which:

FIG. 1 is a block diagram representation of a protection circuitaccording to the invention which is connected to a cellular telephone,

FIG. 2 is a more detailed representation of the protection circuit shownin FIG. 1, and

FIG. 3 is a schematic representation of a protection circuit which isprovided in combination with a battery, for use with a cellulartelephone, and encapsulated, as an integral unit, in an insulatingmaterial.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 of the accompanying drawings illustrates in block diagram form aprotection circuit 10, according to the invention, which is connected toa cellular telephone 12.

The protection circuit is provided in combination with a battery 14,i.e. as an integral unit. The battery is used for powering the cellulartelephone.

The battery supplies power to the components of the circuit 10 through athermal and current fuse 16 and current limiting resistor 18.

The circuit includes an over-voltage detecting unit 20, a unit 22 fordetecting excess current supplied by the battery, a first controlintegrated circuit 24, a second control integrated circuit 26 whichincludes onboard memory 28, and a temperature sensor 30.

The cellular phone includes an on board memory 32 which is also referredto as a flash integrated circuit. The memory 32 is conventional and issupplied as original equipment in the cellular telephone. The capacityof the memory 32 is generally substantially in excess of what isrequired for operating the cellular telephone. The interaction of thecellular telephone with the flash integrated circuit is known in the artand is not further described herein. It is however possible, for aperson skilled in the art, to access the memory 32 and store code, i.e.computer software, in the memory.

The battery 14 is carefully selected according to predetermined criteriato provide a maximum extent of inherent safety protection, in use withthe cellular telephone. Preferably use is made of a manganese dioxidebattery of a type which is sold by NEC and which has the capability ofwithstanding a short circuit condition, in the absence of a protectioncircuit, without exploding. Details of the battery type are recorded asidentity data which is unique to the battery. The identity data is thenentered into the memory 32 where the data is permanently stored.

It is to be understood that the identity data can take on any suitableformat and may comprise a string of characters of suitable length toensure that the data is, a matter of fact and for all practicalpurposes, unique and pertains only to the chosen battery type.

The same identity data is entered into, and is permanently stored in,the memory 28.

It is to be understood that the second control integrated circuit 26 hasonboard intelligence and is capable of executing software instructions.

The protection circuit 10 includes output terminals 34 which can makeelectrical contact with corresponding contacts 36 on the cellulartelephone 12. This aspect is of course known in the art.

The battery 14 and the fuse 16 are connected to the remainder of theprotection circuit 10 through terminals 38.

The fuse 16 is physically positioned so that it is in close proximity tothe cellular telephone 12. This characteristic is designated by means ofa dotted line 40.

The temperature sensor 30 has the capability of sensing the temperatureof a charger 42 which may be used, from time to time, to recharge thebattery 14. This aspect is known in the art and is not further describedherein. It is pointed out however that the charger 42 does not form partof the protection circuit 10.

The components to the left of the terminals 34, i.e. the battery 14 andthe protection circuit 10, but excluding the charger 42, areencapsulated in an insulating material such as a polyurethane resin. Theterminals 34 are exposed so that they can make electrical contact withthe contacts 36.

When the encapsulated components are connected to the cellular telephone12 the second control integrated circuit 26 interrogates the memory 32and reads the stored data therein which relates to the identity of thebattery 14, which is permitted to be used with the cellular telephone12. The data which is read from the memory 32 is compared by the circuit26 to the data which is held in the onboard memory 28 and which uniquelyidentifies the battery 14. If the data in the memory 32 corresponds withthe data in the memory 28 then this is taken as positively indicatingthat the battery 14 can, as a matter of fact, be used with the cellulartelephone 12 and the electrical connection between the protectioncircuit 10 and the cellular telephone 12 is maintained. It is thereforepossible to operate the cellular telephone with power being provided bythe battery 14. If however the comparison process shows that the data inthe memory 32 does not correspond with the data in the memory 28 then itis taken that the battery 14 may not be used with the cellular telephone12 and the circuit 26 automatically and immediately interrupts thesupply of power from the battery to the cellular telephone.

The current which is supplied by the battery 14 to the remainder of thecircuitry passes through the fuse 16. The fuse also senses thetemperature of the cellular telephone 12. If the supplied current, orthe temperature of the cellular telephone 12, is too high then the fusefuses and opens circuits the path between the battery and the remainderof the circuit.

The resistor 18 is a current limiting resistor which has considerablepower handling capacity. Thus the resistor 18 is used to limit currentwhich is supplied by the battery to the circuit 10, in order to preventany component in the circuit 10 from fusing. On the other hand therating of the resistor 18 is such that, even if an over-currentsituation does occur, the resistor will not fuse. Fusing of electricalcomponents is to be avoided as far as is possible, for fusing inevitablyresults in localised high temperatures which can be dangerous in ahazardous atmosphere.

The first control integrated circuit 24 is responsive to the voltageunit 20 and the current unit 22. The former unit monitors the voltagesupplied by the battery 14 and limits this voltage in the event thevoltage exceeds a safe value. The current unit 22 monitors currentcharge and current discharge rates when the battery 14 is recharged bythe charger 42 or is drained, during usage. In each case if the currentflow rate is too high the unit acts to limit or interrupt the currentflow.

The temperature sensor 30, as has been indicated, monitors thetemperature of a charger 42 when this is used to recharge the battery14. If the charger temperature goes too high then the control circuit26, which is responsive to the temperature sensor open-circuits at leastthe connection between the charger and the battery so that thetemperature of the charger is limited.

FIG. 3 illustrates a physical embodiment of the arrangement shown inFIG. 1. The cellular telephone 12 is shown schematically with thecontacts 36 on an external surface thereof. The battery 14 and theprotection circuit 10 are provided as an integral package and areencapsulated in an insulating material 40 such as a polyurethane resin.The protection circuit 10 is, prior to being embedded in the resin 40,separately embedded in an insulating material 52. In other words thecircuit 10 is effectively embedded in two volumes of insulatingmaterial.

The terminals 34 are at an upper end of the assembly and are positionedso that they can be brought into electrical contact with the contacts 36on the cellular telephone 12 when the assembly is engaged with thetelephone.

The fuse 16 is physically and electrically connected between the batteryand the circuit 10. It follows that when the fuse 16 is fused, due to anover-temperature or over-current condition, it is not possiblethereafter to effect an electrical connection between the circuit 10 andthe battery 14 for the insulating resin prevents access to electricalcontact points on the battery and on the circuit.

The battery 14, as has been noted, is preferably a manganese dioxidebattery of the type sold by NEC. This battery has a hydrogen gas ventpoint or cap 54 which is positioned at a lower region of the assembly sothat hydrogen gas which is generated through use of the battery candischarge to atmosphere and does not pressurise the interior of theencapsulating resin.

The battery 14 and the circuit 10 are held in contact with the cellulartelephone 12 by means of suitable clips (not shown) which act in amanner known in the art.

FIG. 2 is a circuit diagram of the arrangement shown in FIG. 1. Whereapplicable components which are the same as shown in FIG. 1 bear likereference numbers to what has been employed in FIG. 1. The cellulartelephone is not shown in FIG. 2. It is connected to the terminalsmarked 34. The protection integrated circuit 24 is, for example, aMitsumi MM1491 IC. The function of this integrate circuit is to monitorthe current which is delivered by the battery 14 as well as the voltageacross the protection circuit 10. The voltage unit 20 includes a fieldeffect transistor arrangement comprising, for example, a pair of Toshibasilicon N-channel Mosfets TPC 8204. The current unit 22, in thisexample, comprises an NPN Darlington transistor pair which acts as anhigh input preamplifier.

The second protection integrated circuit 26 is a micro controller and,for example, may be an ACE 0010E micro controller. This micro controlleris employed for battery identification and recognition and, as stated,includes software so the cellular telephone can only be operated by thebattery 14 if the identity of the battery indicates that the battery 14is a permissible or allowed battery.

The temperature sensor 30 is conveniently a thermistor in the form of a47K negative temperature coefficient (NTC) thermistor. The thermistormonitors the temperature of the battery 14 or of the charger 42 which isused for recharging the battery.

A contact terminal 60 is provided on the circuit 10. The arrangement issuch that when the battery and protection circuit pack is connected tothe cellular telephone the terminal 60 makes contact with acorresponding terminal, not shown, on the cellular telephone so that itis possible for data to be interchanged between the micro controller 26and the flash memory in the cellular telephone, in the manner which hasbeen described hereinbefore. This procedure permits the battery type tobe identified.

On the other hand when the battery is being charged by means of thecharger 42 the contact 60 permits the temperature of the charger to besensed and relevant data is fed to the micro controller 26 whichmonitors the process and which is capable of open-circuiting connectionsif the temperature rises above a predetermined limit.

The circuit 10 is mounted on a printed circuit board, not shown. The PCboard has specified track width and spacing. In general the minimumtrack spacing allowed, i.e. the track clearance, is 0.5 mm separationdistance through solid and casting compound. On the other hand theminimum track width is 0.2 mm allowing a maximum permissible current of1.8 Amps for temperature ranges between 100° C. to 450° C., and 1.3 Ampsfor 85° C.

If an over-voltage condition is detected by the voltage unit 20 then theprotection integrated circuit 24 can open circuit the battery connectionto the remainder of the protection circuit 10 or alternatively can actto regulate the voltage. Similarly, a high or unwanted charge ordischarge current will be detected by the current unit 22 which will actto regulate the current or to open circuit the connection between thebattery and the remainder of the circuit 10.

The micro controller 26 is, as has been indicated, responsive to theidentification process relating to the battery type and to thetemperature of the charger, when it is used. When an unwanted conditionoccurs, from either of these causes, the circuit 26 changes the bias onthe transistor pair 22 and the protection circuit 24 open circuits.

The battery 14 is housed in a case which typically has an ingressprotection of at least 20 which means that it is mechanically protectedagainst solid objects with a size in excess of 12 mm. The insulatingmaterial in which the battery is encapsulated has a surface resistanceof less than 1G Ohm which ensures that the likelihood of staticelectricity, would could serve as an explosive ignition source, is muchreduced.

1. A protection circuit (10) for a battery (14) used with a cellulartelephone, the protection circuit comprising: a first memory (28)storing first data which identifies the battery; a second memory (32)for storing second data associated with the telephone and whichidentifies a battery which is permitted to be used with the telephone; afirst software driven controller (26) for comparing the first data tosaid second data; and a switch responsive to the controller (38) forconnecting the battery to the telephone; wherein the protection circuit(110) is encapsulated in an insulating material, is provided incombination, as an integral unit with the battery (14) and iselectrically connected to the battery (14) by means of a thermal fuse(16), wherein the first controller (26) causes the switch to connect thebattery to the telephone only if the first data corresponds to thesecond data.
 2. The protection circuit according to claim 1, furthercomprising: a sensor (30) for monitoring the temperature of a charger(42) which is used for recharging the battery (14), and for monitoringthe temperature of the battery (14); wherein the first controller (26)is responsive to the sensor and is operable, when either of themonitored temperatures exceeds a predetermined temperature, to carry outat least one of disconnecting the battery from the charger, anddisconnecting the battery from the telephone.
 3. The protection circuitaccording to claim 1, further comprising a second controller (24)operable to disconnect the battery from the telephone upon theoccurrence of at least one of the battery voltage exceeding apredetermined voltage; and the current drawn from the battery exceeds apredetermined current.
 4. A protection circuit in combination with acellular telephone battery comprising: a cellular telephone battery; aprotection circuit having a first memory for storing first dataidentifying the battery and a first controller for comparing the firstdata to second data stored in a second memory, the second data relatingto the telephone and identifying a battery type permitted to be usedwith the telephone, and a switch responsive to the controller forconnecting the battery to the telephone, said first controller causingsaid switch to connect the battery to the telephone when said first datacorresponds to said second data; wherein the protection circuit (110)and the battery (14) are combined as an integral unit and encapsulatedin an insulating material.
 5. The combination according to claim 4,further comprising a thermal fuse electrically connecting said batteryand said protection circuit.
 6. The combination according to claim 4,further comprising a second controller operable to disconnect thebattery from the telephone upon the occurrence of at least one of: thebattery voltage exceeding a predetermined voltage, and the current drawnfrom the battery exceeds a predetermined current.